An RF connector, sometimes called a coaxial connector, is that part of an electrical signal transmission system which allows for the coupling and uncoupling of system-interconnecting conductors forming part of printed circuit boards (PCBs), RF modules, coaxial cables and so forth. For example, in many apparatus flexible or semirigid coaxial cables of small diameter (less than 1/8-inch) are used to transmit RF signals having frequencies exceeding 10 GHz. As is well known, such coaxial cables comprise an inner or center wire conductor disposed coaxially within a shielding outer tubular conductor with a dielectric or insulating material interposed between the inner and outer conductors. To avoid degradation of the quality of the RF signal being transmitted, connectors used to couple coaxial cables should present to the signal the same characteristic impedance as the cables and should minimize losses in the continuity of the electric field developed by the signals being transmitted.
Known high frequency signal coaxial connectors typically include a pair of connector elements adapted to be releasably coupled, one referred to as the receptacle or jack and the other as the plug. These elements are of generally cylindrical shape and include a central contact (in the form of either a socket or pin) and an outer tubular conductor separated by an insulating or dielectric sleeve. The jack and plug connector elements have mateable end portions whose construction is critical to minimizing signal degradation and/or loss.
In accordance with one known construction, exemplified by U.S. Pat. Nos. 5,074,809; 5,474,470; and 4,690,482, the plug includes an outer tubular conductor having a male contact portion that is slotted so as to define spring contact fingers. The receptacle connector element includes a tubular outer conductor housing whose inner surface comprises a female contact part for receiving the male contact part of the plug connector element. To assure good electrical contact between the contact parts of the plug and receptacle, the spring contact fingers on the plug may be spread or flared outwardly and/or provided with outwardly extending projections adjacent to the extremities of the fingers. Such conventional RF coaxial connectors have several disadvantages, stemming principally from discontinuities in the plug and jack assembly resulting in RF signal degradation and/or loss. These RF coaxial connectors also tend to be relatively large and complex.
FIGS. 1-11 show details of common types of conventional, prior art subminiature RF coaxial connectors. With reference first to FIGS. 1-4, there is shown a prior art coaxial connector 10 including a jack 12 and a plug 14 adapted to be coupled or assembled so as to interconnect a pair of coaxial cables (not shown) the ends of respective ones of which are attached to the jack and plug in a manner well known in the art.
The jack 12 includes a generally tubular outer conductive housing 16 having an outer surface 18 and a mateable end portion 20 provided with a plurality of longitudinally extending slots 22 (typically 4 in number) thereby defining a plurality of finger contacts or beams 24. The outer surface 18 of the housing 16 is stepped so as to define a radially extending abutment surface 26 rearward of the roots of the beams 24. The mateable end portion 20 has a forward extremity 28. Bevels 30 at the forward ends of the beams 24 facilitate assembly of the jack 12 and plug 14. The outer surfaces of the beams 24 and the bevels 30 intersect at an edge 32. Disposed within the mateable end portion 20 of the jack is an insulating or dielectric sleeve 34 having a front face 36 coplanar with the forward extremity 28 of the end portion 20. The sleeve 34 includes a central bore 38 for receiving a center contact which has been omitted for clarity.
The plug 14 includes a generally tubular outer conductive housing 40 having an inner wall 42 of diameter D2 and a front annular face 44. Disposed within the housing 40 is an insulative or dielectric sleeve 46 having a central bore 47 for receiving a center contact (not shown) and a planar front surface 48 set back from the end face 44 so as to define a mateable end portion 50 of the plug 14.
As shown in FIG. 2, the beams 24 are spread or flared radially outwardly. Before the beams 24 are flared, the mating outside diameter (D1 in FIG. 1) of the jack 12 is a clearance fit with the mating inside diameter (D2) of the inner wall 42 of the plug outer conductor 40. The beams 24 of the jack 12 must be flared radially outward to dimension A (where A is greater than D2) to assure electrical contact with the inner surface 42 of the mating plug 14. The flaring operation, however, adds one dimension and an associated tolerance along with an additional tolerance for the symmetry of the flare. When the prior artjack 12 and plug 14 are mated (FIGS. 3 and 4), the beams 24 deflect radially inward. Electrical contact between the jack and plug outer conductors 16 and 40 occurs between arcuate portions of the edge 32 at the extreme front of the jack beams 24 and the inner wall 42 of the plug outer conductor 40. The abutment surface 26 on the outer housing 16 of the jack functions as a mechanical stop engaged by the front face 44 of the plug outer conductor 40 and defines the length of a coax interface gap 52 (FIG. 4) when the jack 12 and plug 14 are fully mated. The abutment surface 26 has no electrical function except the possible reduction of RF leakage when the surfaces 26 and 44 are in engagement. There are no electrical butt-mating surfaces at the coax interface; instead a gap, such as the gap 52, is intentionally provided to produce an inductance to offset the capacitance produced by the difference between the diameters of the dielectric sleeves 34 and 46.
Since the inside diameter (D2) of the plug outer conductor housing 40 is larger than the outside diameter (D1) of the mating portion 20 of the jack outer conductor housing 16, the diameter of the center bore 47 of the plug dielectric sleeve 46 must be larger than the diameter of the center bore 38 of the jack dielectric sleeve 34 in order for the impedance of the plug and jack to be equal. These step changes across the mated interface make the gap 52 necessary to minimize RF losses. However, at higher frequencies (f.gtoreq.10 GHz), despite the attempt to compensate for the step changes at the interface, significant RF losses remain.
With reference now also to FIGS. 9-11, for the connector shown in FIGS. 1-4, circumferential contact between the outer conductor housings 16 and 40 occurs only at arc segments where the front edges 32 of the beams 24 contact the mating inner wall 42 of the plug 14. In FIGS. 9 and 10, the arc segments along which contact occurs are designated by X while the arc segments along which there is no contact arc denoted by Y; it will be seen that Y is substantially greater than X. Nor is there any contact along the longitudinally extending edges 23 of the beam slots 22 (FIGS. 9 and 10). The signal current patterns that are understood to be produced in this connector are depicted by the broken lines in FIGS. 10 and 11. The substantial areas of electrical discontinuities will be apparent from these Figures.
If the beams 24 are not flared radially outward as shown in FIG. 2, the configuration of the plug or jack of the prior art must be altered in some way to assure electrical contact between the outer conductor housings 16 and 40 when the plug and jack are mated. Two examples follow and each has the disadvantages described with reference to the prior art embodiment of FIGS. 1-4.
With reference first to prior art FIGS. 5 and 6, a raised projection or ridge 56 may be added to the outer surface of each jack beam 24 adjacent to the forward extremity 28. The outside diameter (D3) of the ridge 56 must be larger than the mating inner diameter (D2) of the plug 14. The outside surface of the jack dielectric sleeve 34 in the area under the beams 24 must be relieved to provide an annular clearance 58 for beam deflection when the plug and jack are mated. Electrical contact is maintained along the line of contact between the ridge 56 and the inner wall 42 of the plug housing 40.
With reference to FIGS. 7 and 8 showing yet another prior art connector, the mating portion 50 of the plug 14 may be tapered outwardly toward the front extremity 44 at an angle .theta. from a root diameter (D4). The angle .theta. is greater than the final angle of deflection .phi. of the beams 24 of the jack to assure that electrical contact is maintained at the extreme front edge of the jack beams when the plug and jack are fully mated. As in the example of FIGS. 5 and 6, the jack dielectric sleeve 34 must be relieved to provide an annular clearance 58 to accommodate beam deflection.
Thus, an overall object of the present invention is to provide an improved ultra high frequency connector that significantly decreases RF signal losses and degradation.
Another object of the present invention is to provide a connector that is relatively simple, comprising few parts, and that can be made small enough so that an array of such connectors may be mounted side-by-side on standard 0.100-inch centers so that they can be incorporated in standard, multicontact insulating connector bodies or can be used to interconnect printed circuit boards, for example.